90/90 or Active Knee Extension (AKE) Hamstring Flexibility Test Calculator

The 90/90 test, also known as the Active Knee Extension (AKE) Hamstring Flexibility Test, measures hamstring flexibility, particularly when the hip is flexed. This test is essential for athletes in running, kicking, and jumping sports where dynamic hamstring flexibility directly impacts performance and injury risk.

How to Use the Hamstring Flexibility Calculator

Follow these simple steps to calculate and interpret your hamstring flexibility:

1. Perform the 90/90 Test
   • Lie supine (on your back) with one hip and knee flexed to 90°
   • Keep the opposite leg flat on the table, fully extended
   • Actively extend the knee of the raised leg as far as possible
   • Maintain the thigh in vertical position throughout
2. Measure Your Angle
   • Use a goniometer or smartphone app to measure knee flexion angle
   • Measure at the point of first firm resistance
   • Record the angle in degrees (0° = fully straight)
3. Enter Data and Calculate
   • Input your measured knee flexion angle
   • Click "Calculate Flexibility" for instant results
4. Understand Your Results
   • Review your flexibility category (Excellent to Poor)
   • Compare to athlete normative data
   • Follow personalized training recommendations

Understanding the 90/90 Hamstring Flexibility Test

The 90/90 test is a validated clinical assessment measuring hamstring muscle length in a functionally relevant position. Unlike the traditional sit-and-reach test which also involves lower back flexibility, the AKE test isolates hamstring extensibility by stabilizing the hip joint at 90 degrees of flexion.

Why This Test Matters for Athletes

Hamstring flexibility in the 90/90 position specifically relates to athletic movements that occur with a flexed hip, including:

• Sprinting and Running: During the late swing phase, the hamstrings must lengthen while the hip is flexed
• Kicking: Soccer players, martial artists, and football punters need hamstring flexibility in hip flexion
• Jumping: Basketball and volleyball players require flexibility for optimal takeoff mechanics
• Hurdling: Track athletes need exceptional flexibility for lead leg clearance

Research by Malliaropoulos et al. (2015) found that elite track and field athletes demonstrate mean knee extension angles of 72.3° to 73.9°, which translates to approximately 17-18° of remaining knee flexion. Athletes with greater hamstring flexibility in this test position show better performance in speed and power events.

Test Reliability and Validity

The Active Knee Extension test demonstrates excellent psychometric properties:

• Intra-rater reliability: ICC = 0.86-0.99 (excellent)
• Inter-rater reliability: ICC = 0.76-0.89 (good to excellent)
• Standard error of measurement: 3.3-4.0 degrees
• Minimal detectable change: 9-11 degrees

Studies have confirmed the AKE test isolates hamstring flexibility better than the straight leg raise or sit-and-reach tests, making it the preferred assessment for athletes and clinical populations.

The Science Behind Hamstring Flexibility Assessment

What We're Actually Measuring

The 90/90 test measures the knee extension angle achieved when the hip is stabilized at 90° of flexion. This angle reflects:

• Hamstring muscle extensibility (semitendinosus, semimembranosus, biceps femoris)
• Neural tissue mobility along the sciatic nerve pathway
• Myofascial restrictions in the posterior thigh

Interpretation Formula: Lower angles indicate better flexibility. An angle of 0° means you can fully extend your knee with the hip flexed (exceptional flexibility). Each degree of remaining flexion represents that amount of restriction in hamstring length.

Normative Values for Different Populations

Calculation Example: Sprint Athlete Assessment

Let's walk through interpreting results for a competitive sprinter:

Measured Values:

• Knee flexion angle: 18°
• Gender: Male
• Sport: Sprinting
• Level: Competitive

Step 1: Compare to normative data → 18° falls in "Good" range (15-20°)
Step 2: Calculate extension achieved → 90° - 18° = 72° of extension
Step 3: Athletic comparison → Slightly below elite sprinters (typically 5-15°)
Result: Good flexibility for competitive level, but room for improvement to reach elite standards

Accuracy and Limitations

The 90/90 test provides estimates with approximately ±3-4° accuracy for active populations when proper technique is used. Factors affecting accuracy include:

• Pelvic positioning: Must maintain neutral lumbar spine
• Hip angle control: Thigh must stay vertical throughout
• Neural tension: May limit range independent of muscle length
• Time of day: Flexibility typically better in afternoon/evening

For clinical diagnosis or elite athlete monitoring, this test should be combined with other assessments including strength testing, movement screening, and sport-specific evaluation.

Sport-Specific Applications of Hamstring Flexibility

Track and Field Athletes

Sprinting Events (100m-400m)

• Optimal range: 10-18° knee flexion
• Elite sprinters: Often achieve 5-12° (exceptional flexibility)
• Performance impact: Better flexibility correlates with longer stride length
• Training focus: Dynamic flexibility and sprint-specific strength

Hurdling

• Optimal range: 5-15° (requires superior flexibility)
• Lead leg clearance demands extreme hamstring length
• Trail leg also requires significant flexibility for efficient technique
• Training focus: Active flexibility with hurdle-specific drills

Jumping Events (Long Jump, Triple Jump, High Jump)

• Optimal range: 10-20° knee flexion
• Takeoff mechanics benefit from balanced flexibility and power
• Position-specific: High jumpers need flexibility for back arch technique
• Training focus: Explosive power maintenance with flexibility work

Soccer and Football

Soccer Players

• Optimal range: 15-25° knee flexion varies by position
• Strikers/Forwards: Better flexibility (12-20°) enhances shooting power
• Defenders: Functional range (18-25°) adequate for position demands
• Performance impact: Kicking velocity correlates with hamstring flexibility

American Football

• Wide Receivers: 15-22° for route running and jumping
• Running Backs: 18-25° balances flexibility with power production
• Kickers/Punters: 8-18° (exceptional flexibility required)
• Training consideration: Heavy strength training can reduce flexibility

Basketball and Volleyball

Court Athletes

• Optimal range: 15-22° knee flexion for jumping sports
• Vertical jump performance shows moderate correlation with flexibility
• Landing mechanics: Better flexibility may reduce knee injury risk
• Position variations: Guards may need slightly better flexibility than posts

Cycling and Endurance Sports

Cyclists

• Adequate range: 20-30° (less demand than running sports)
• Aero position: Some tightness actually beneficial for aggressive positioning
• Lower back: Flexibility more critical than hamstring length
• Training note: Extended time in flexed position can reduce flexibility

Distance Runners

• Optimal range: 15-25° knee flexion
• Efficiency: Moderate flexibility optimal (not maximum flexibility)
• Injury prevention: Values >30° associated with increased injury risk
• Training balance: Flexibility work 2-3x weekly during high mileage phases

Martial Arts

Kicking Sports (Taekwondo, Karate, Kickboxing)

• Optimal range: 5-15° (exceptional flexibility required)
• High kicks demand extreme hamstring length in hip flexion
• Elite practitioners: Often achieve 0-8° (can extend knee fully)
• Training focus: Daily flexibility work essential for technique execution

How to Improve Your 90/90 Test Score

Evidence-Based Flexibility Training Protocols

Research demonstrates that consistent flexibility training can improve 90/90 test scores by 10-15° over 6-8 weeks. A study by Nelson and Bandy (2004) found that both static stretching and eccentric training produced similar gains of approximately 12° in high school athletes.

Training Frequency Recommendations:

Effective Stretching Techniques for Hamstring Flexibility

1. Static 90/90 Hamstring Stretch

• Position: Same as test position - hip flexed 90°, actively extend knee
• Hold: 30-60 seconds per leg
• Progression: Gradually increase knee extension over time
• Reps: 2-3 repetitions per leg

2. Supine Single-Leg Hamstring Stretch with Strap

• Position: Lie on back, wrap strap around foot, keep knee straight
• Action: Pull leg toward chest until gentle stretch felt
• Hold: 30-45 seconds per leg
• Benefits: Can achieve deeper stretch than unassisted

3. Standing Forward Bend

• Position: Feet hip-width apart, hinge at hips keeping back straight
• Hold: 30 seconds, repeat 3-4 times
• Modification: Slight knee bend if needed initially
• Progression: Gradually straighten legs more as flexibility improves

4. Eccentric Nordic Hamstring Curls

• Position: Kneeling with ankles secured, slowly lower body forward
• Action: Control descent with hamstrings for 5-8 seconds
• Reps: 3 sets of 6-8 repetitions
• Benefits: Strengthens while improving flexibility (research-proven)

5. Dynamic Leg Swings

• Position: Standing, swing one leg forward and back
• Range: Gradually increase height with control
• Reps: 10-15 swings per leg
• Timing: Best as pre-activity warm-up

Training Programming for Athletes

Off-Season Flexibility Development (8-12 weeks):

• Frequency: 5-6 sessions per week
• Static stretching: 3-4 sessions (30-60 sec holds)
• Eccentric training: 2-3 sessions (Nordic curls, RDLs)
• PNF stretching: 1-2 sessions with partner
• Goal: Improve baseline flexibility by 10-15°

In-Season Maintenance (during competition):

• Frequency: 3-4 sessions per week
• Pre-training: Dynamic stretching and leg swings (5-8 min)
• Post-training: Static stretching when muscles warm (10-15 min)
• Recovery days: Extended stretching sessions (20-30 min)
• Goal: Maintain pre-season range without compromising power

Addressing Neural Tension

If flexibility improvements plateau despite consistent stretching, neural tension along the sciatic nerve may be limiting range. Indicators include:

• Burning or tingling sensation during stretch
• Pain radiating down leg rather than isolated muscle stretch
• Symptoms that change with neck position (neural signs)
• Asymmetry between legs despite equal training

Neural Gliding Exercises (if neural tension suspected):

• Perform under guidance of sports therapist or physiotherapist
• Gentle, rhythmic movements rather than sustained holds
• Should not reproduce sharp or radiating pain
• May unlock flexibility gains when muscle stretching plateaus

Test Procedure and Protocol

Test purpose: to assess the range of active knee extension in a position of hip flexion, as required in running and kicking.

Equipment required: goniometer with extended arms and spirit level (optional), and a firm table.

Pre-test: Explain the test procedures to the subject. Perform screening of health risks and obtain informed consent. Prepare forms and record basic information such as age, height, body weight, gender and test conditions. See more details of pre-test procedures.

Procedure: The subject lies supine, head back and arms across the chest. The hip is passively flexed until the thigh is vertical (use a spirit level if available). Maintain this thigh position throughout the test, with the opposite leg in a fully extended position. The foot of the leg being tested is kept relaxed, while the leg is actively straightened until the point when the thigh begins to move from the vertical position. The thigh angle at this point is recorded.

Measurement: measure the minimum angle of knee flexion with the thigh in the vertical position. The measurement unit is degrees. If the leg is able to be fully straightened, the angle would be recorded as 0. Any degree of flexion will be recorded as a positive number, e.g. 10, 20 degrees etc. In cases where the full knee extension is achieved without thigh movement, the knee is flexed and the thigh is moved to 30 degrees past the vertical position, and the knee again straightened. The angle of knee flexion at which the thigh begins to move is again recorded.

Similar Tests

• Straight Leg Raise Test
• Sit and Reach Test

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